1. Field of the Invention
The present invention relates to a projection exposure apparatus, e.g., provided in an environmental chamber connected to an air-conditioning mechanism for manufacturing semiconductor devices, liquid crystal display devices, etc. to a method of controlling optical performance in a projection exposure apparatus, and to a method for making a lithographic system.
2. Related Background Art
In manufacturing semiconductor devices, liquid crystal display devices, etc. in photolithography processes, projection exposure apparatuses are used in which the image of a pattern of a photomask or a reticle (hereinafter referred to as the reticle) is exposed on a wafer (or a glass plate) with photoresist applied thereto.
FIG. 3 shows a conventional projection exposure apparatus. Exposure light IL from an illumination optical system 1 illuminates a pattern on a reticle 2 supported by a reticle stage 3 with a uniform illuminance distribution. A projection optical system 4 is disposed under the reticle stage 3. A correction optical member 7 for correcting the telecentric characteristic of the projection optical system 4 is mounted on the reticle side of the projection optical system 4 via supporting frames 5A, 5B and driving sections 6A, 6B. The telecentric characteristic of the projection optical system PL can be corrected by correcting the position of the correction optical member 7 in the optical axis direction or the inclination thereof via the driving sections 6A, 6B.
Under the exposure light IL, the pattern of the reticle 2 is projected and exposed via the projection optical system 4 on each shot area on a wafer 8 supported by a wafer stage 9. At this time, the projected image on the wafer 8 includes various aberrations in accordance with the change in atmospheric pressure in the projection optical system PL. That is, the projection optical system 4 is designed under a condition that the atmospheric pressure is a predetermined value. Therefore, when the atmospheric pressure in the projection optical system 4 is changed from the predetermined value, the refractive index of the gas in each space between lenses constituting the projection optical system 4 is changed, resulting in deviations from various design conditions, i.e., changes of imaging characteristics (focal point position, magnification, field curvature, distortion, etc.).
For avoiding this problem, conventionally, the atmospheric pressure in the projection optical system 4 is measured by an atmospheric pressure sensor 10 and the measured value is constantly monitored by a control device 11. Then, the control device 11 adjusts the atmospheric pressure in a space 16 between the n-th lens 14 (n: a predetermined integer) in the projection optical system 4 and the (n+1)-th lens 15 therein via a pressure control unit 12, or changes the position or inclination of the correction optical member 7 by driving the driving sections 6A, 6B of the projection optical system 4 via a drive control device 17 thereby to correct the changes of various aberrations of the projected image due to the change in atmospheric pressure. A method of changing imaging characteristics by controlling the pressure in a specific space between lenses in a projection optical system is disclosed in U.S. Pat. No. 4,666,273. Also, a method of changing imaging characteristics by driving a few lens elements in a projection optical system is disclosed in U.S. Pat. No. 5,117,255.
In the above prior art, the problem of the change in refracting index of the air due to the change in atmospheric pressure is solved by changing the pressure in the specific space between specified lens elements in the projection optical system 4 to change the refractive index of a portion of the air in the projection optical system 4, or changing the distance between the reticle 2 and the wafer 8 or the distance between the lens elements in the projection optical system 4. There are many factors which cause distortion of the projected image due to the projection optical system 4, and allowable ranges of aberrations are limited vary narrowly. For example, as a factor of the distortion of the projected image due to the change in atmospheric pressure, there are aberrations caused by the defocus condition in which the focus position is changed between the reticle and the wafer. As the other aberrations, there are field curvature, comatic aberration, astigmatism, magnification, distortion, etc. Therefore, it becomes difficult to correct all the aberrations of the projected image up to presently required levels only by changing the distance between the reticle 2 and the wafer 8 or changing a portion of lens conditions in the projection optical system 4 (the pressure between lenses, the distance between lenses).
Also, when a laser light source such as an excimer laser is utilized as the light source in the illumination optical system 1, if the wavelength of laser light having a narrow bandwidth is shifted, the same effect as when the atmospheric pressure is changed can be obtained. However, it is difficult to correct the aberrations of the projected image due to the change in atmospheric pressure by adopting this method using present technology. Also, as the wavelength of the laser light is changed, the absorbability of the photoresist on the wafer is also changed.